1. Field of the Invention
The present invention relates to low-temperature sinterable ceramic compositions that can be simultaneously sintered with low melting point metals, such as silver and copper, and to multilayer ceramic substrates using the same.
2. Description of the Related Art
Recently, in information processing apparatus represented by, for example, computers and mobile communication systems, which sustain the information-oriented society, higher information processing speeds, miniaturization, and multifunctionality have progressed significantly. Improvements in performance of the information processing apparatus are primarily realized by use of semiconductor devices, which are highly integrated, and have higher processing speed and improved functionality.
Conventionally, multilayer ceramic substrates are used for mounting semiconductor devices and the like thereon. Multilayer ceramic substrates typically have insulating substrates composed of alumina, which must be baked at 1,500 to 1,600xc2x0 C. In order to be able to simultaneously bake such a substrate with a material used for internal wiring, a high melting point metal, such as molybdenum (Mo), molybdenum-nickel (Moxe2x80x94Ni), or tungsten (W), must be used as the material for the internal wiring. However, these high melting point metals mentioned above have high resistivities and make it more difficult to fully exploit the performance of the semiconductor devices. Thus, higher information processing speed and highly dense wiring have been difficult to realize.
One insulating material used for the multilayer ceramic substrate described above, a ceramic composition composed of MgO and Al2O3, in which the Al2O3 is primarily composed of the MgOxc2x7Al2O3 phase, is disclosed in Japanese Unexamined Patent Application Publication No. 62-241867. The ceramic composition mentioned above is superior in hydration resistance and heat shock resistance and has a low dielectric constant, low tan xcex4, and high thermal conductivity.
However, since the ceramic composition described above has a high baking temperature of 1,500 to 1,600xc2x0 C., as is the case with the insulating substrate composed of alumina described above, a high melting point metal, such as Mo, Moxe2x80x94Ni, or W, must be used as a wiring material for simultaneous baking, whereby there have been limitations on the speed and wiring density that could be obtained.
When a glass component is added to the ceramic composition described above as a sintering auxiliary, the sintering temperature can be decreased; however, depending on the glass component to be used, the strength of the multilayer ceramic substrate may be significantly decreased in some cases. On the other hand, if the strength of the multilayer ceramic substrate is maintained, the Q value may decrease or the dielectric constant may vary, and hence, the characteristics of the substrate may be degraded in some cases.
Taking into consideration the problems described above, the present invention provides a low-temperature sinterable ceramic composition having an advantageous combination of high strength and superior electrical characteristics, with which a low melting point metal, such as silver or copper, can be simultaneously sintered. The invention also provides a multilayer ceramic substrate using the composition.
Through intensive research by the inventor of the present invention to solve the problems described above, it was discovered that a low-temperature sinterable ceramic composition having desired strength and superior electrical characteristics can be obtained by adding a glass component having a specified composition on a weight ratio basis to a ceramic component having an MgO crystal phase and an MgAl2O4 crystal phase, followed by mixing.
That is, a low-temperature sinterable ceramic composition of the present invention comprises a ceramic component comprising an MgO crystal phase and an MgAl2O4 crystal phase and a glass component composed of 13 to 50 wt % silicon oxide, 3 to 30 wt % boron oxide, and 40 to 80 wt % alkaline earth oxide.
In the low-temperature sinterable ceramic composition of the present invention, the glass component may further comprise 10 wt % or less alkali metal oxide.
In the low-temperature sinterable ceramic composition of the present invention, 20 to 80 parts by weight of the glass component may be added to 100 parts by weight of the ceramic component.
In the low-temperature sinterable ceramic composition of the present invention, when the ceramic component is represented by the formula xMgOxe2x80x94yMgAl2O4 on a weight ratio basis, the x and the y may be such that 10xe2x89xa6xxe2x89xa690 and 10xe2x89xa6yxe2x89xa690, in which x+y=100.
The low-temperature sinterable ceramic composition of the present invention may further comprise 3 wt % or less copper oxide.
The low-temperature sinterable ceramic composition of the present invention preferably has a dielectric constant of 9 or less and has a Q value of 400 or more at 10 GHz. In addition, the low-temperature sinterable ceramic composition of the present invention preferably has a flexural strength of 200 MPa or more.
A multilayer ceramic substrate of the present invention comprises an insulating layer composed of the low-temperature sinterable ceramic composition described above and a conductive layer composed of one of a silver-based, a copper-based, and a gold-based conductive material, in which the insulating layer and the conductive layer are laminated with each other.
The multilayer ceramic substrate of the present invention may further comprise a dielectric layer composed of a dielectric ceramic composition formed on the insulating layer by mixing a dielectric ceramic component and a glass component.
According to the low-temperature sinterable ceramic composition of the present invention, a glass component composed of 13 to 50 wt % silicon oxide, 3 to 30 wt % boron oxide, and 40 to 80 wt % alkaline earth oxide is added to and is mixed with a ceramic component having an MgO crystal phase and an MgAl2O4 crystal phase, and hence, a ceramic composition having a preferable combination of high strength and superior electrical characteristics can be realized, and a low melting point metal, such as silver or copper, can be simultaneously sintered therewith.
According to the multilayer ceramic substrate of the present invention, since the insulating layer is formed of the low-temperature sinterable ceramic composition described above, the conductive layer can be formed of a conductive material having relatively low resistivity, such as a silver-based, a copper-based, or a gold-based material, and as a result, a multilayer ceramic substrate having high strength can be realized which has superior electrical characteristics, and in particular, superior high frequency characteristics.